background change when knob is at 21

public/index.html

@@ -16,6 +16,13 @@
           // Listen for custom events from the server
           socket.on('node-data', function(data) {
             console.log(data); // Log the received data to the browser's console
+              if (node === 'node4' && value === '21') {
+          // Change the background color to red
+          document.body.style.backgroundColor = 'red';
+        } else {
+          // Restore the default background color
+          document.body.style.backgroundColor = 'white';
+        }
           });
         </script>
         <script src='socket.io/socket.io.js'></script>